NEWTOWN, Connecticut (USA TODAY) - Gunman Adam Lanza acted alone and didn't conspire with anyone when he killed his mother, Nancy, in their Sandy Hook home Dec. 14 and then slaughtered 26 children and educators at Sandy Hook Elementary School, a Connecticut State Police report released Monday says.

Investigators reported that a review of electronic evidence and digital media that "appeared to belong to the shooter'' showed he had a preoccupation with mass shootings, particularly the Columbine High School shootings in Littleton, Colo., in 1999.

The summary report by the lead investigator, State's Attorney Stephen Sedensky III, says Lanza shot his way into the school and first killed Principal Dawn Hochsprung and school psychologist Mary Sherlach in the north hallway.

Lanza also shot two other staff members in the hallway who survived.

He then went into two classrooms and killed 20 children and four teachers.

Lanza, 20, used a Bushmaster XM15-E2S rifle to kill the victims at Sandy Hook school before killing himself there with a Glock 10mm handgun. He killed his mother in her bed with a .22-caliber rifle.

The Connecticut State Police's full evidence file about the shootings, which may total thousands of pages, was not released Monday by Sedensky.

The summary report said someone in near the Lanza's Sandy Hook home heard two or three gunshots between 8 a.m. and 9 a.m. on Dec. 14. The person thought the shots were from hunters, though they sounded ''unusually close,'' the report says.

Nancy Lanza was later found dead by police in her bed, and the rifle used to kill her was on the floor next to the bed.

The report details the actions of Lanza when he arrived at Sandy Hook school. He first parked his 2010 Honda Civic next to a No Parking zone outside the school and approached the front entrance just after 9:30 a.m. He was armed with the Bushmaster XM 15-E2S rifle, a Glock 10 mm handgun, a Sig Sauer 9 mm pistol and a large supply of ammunition.

Finding the school doors locked, Lanza shot his way into the building through the plate glass window to the right of the front lobby doors.

The school's main office staff reported glass breaking at about 9:35 a.m. and saw the shooter, "a white male with a hat and sunglasses," carrying a rifle, the report says.

"The shooter walked normally, did not say anything and appeared to be breathing normally," the report says.

Police found numerous violent video games in the basement of the Lanza home.

"The vast majority" of people who knew Lanza and were interviewed by police said they had no explanation for the shooter's actions, the report says.

The autopsy performed on Nancy Lanza determined that the cause of death was multiple gunshots to the head, the report says. An autopsy of Adam Lanza on the same day revealed that Lanza was 6-foot-tall and weighed 112 pounds. No drugs were found in his system..

With the release of the summary report, "the investigation is closed, and no additional release of information or documents by this office is anticipated," Sedensky said in a written statement Monday.

He also didn't release recordings of 911 emergency calls of Dec. 14. Their release was recommended by a state Freedom of Information Commission in September, but Sedensky, in an attempt to protect victims' families, has gone to court to stop the release.

Victims' families read the summary report before it was publicly released Monday.

Donna Soto, whose daughter, Victoria, was a teacher slain at Sandy Hook school, released a statement on her Facebook page prior to the public release.

Donna Soto said the report "is yet another blow that our family has been dealt" and does not answer the family's questions.

"How can we live without Vicki? How do we celebrate Christmas without Vicki? How do we go on every day missing a piece of our family?"

Soto said her family cannot make sense of why the shootings happened and doesn't know if anyone will find answers.

"We don't know if we will ever be whole again," Soto said. "We don't know if we will go a day without pain, we don't know if anything will ever make sense again. We do know that we will stick together, and we will be strong, and we will live, laugh and love as Vicki would want us to."

The Dec. 14 shootings shattered the small, close-knit western Connecticut community and raised several national issues. President Obama went to Newtown Dec. 16 to comfort families who lost a loved one and then pushed for new gun-control laws. Proposed legislation was not passed by Congress, but Connecticut and some other states implemented stricter gun laws.

The shootings also prompted many communities to take steps to make schools more secure and began debates about the effectiveness of the nation's mental health system.

Release of the summary report follows a months-long debate among Connecticut officials, media outlets, open-government advocates and others over the public's right to know and the pain such a report could inflict on families who lost relatives in the shootings.

Newtown residents' opinions are mixed about whether the report should have been released. Many question the timing of the report's release - three days before Newtown families, including returning college students, gather for Thanksgiving and two weeks before the anniversary of the shootings.

Newtown resident Monte Frank says he strongly believes in the First Amendment but questions how much the public needs to know.

"Every time information comes out, it causes pain," says Frank, one of the town's attorneys speaking for himself and not the town. "Hasn't this community suffered enough?"

Frank says, however, that he prefers the immediate release of the report rather than "the slow dribble of information" that is "prolonging the agony and hindering the healing process."

Newtown resident Trish Dardine says the timing of the report's release "is ironic, because I'm sure the media will pick at the report with such vigor that it will look like a turkey carcass the day after Thanksgiving.

"They'll probably be feeding on it when the 12/14 anniversary comes around," Dardine says. "I hope the focus shifts to the larger national issues that are already evident, rather than on how Newtown feels about an unspeakable tragedy on a day we hope to spend in private reflection."

Dardine says, though, she supports release of the report rather than "protracted leaks. Hearing the leaks, whether they are true or not, is like picking at a scab that will never truly heal."

Newtown First Selectman Pat Llodra, the town's chief executive, says the release of the report, the dispute about the 911 recordings and the upcoming anniversary of the Sandy Hook tragedy have combined "to create a layer of anxiety and tension in our community."

They "add to the pain and anguish of the families who lost loved ones," Llodra says.